The present invention relates to composite lens assemblies in general, and to such assemblies in which plastic lens elements are adhesively bonded to other plastic lens elements or to glass elements, in particular.
Owing to the fact that plastic lenses possess certain optical qualities, e.g., low light absorption, wide ranges of refractive indices, low weight, susceptibility to mass production at low cost, etc., which cannot readily be matched by glass lenses, it is sometimes desirable or even necessary to assemble plastic lens elements with glass lens elements into symbiotic units of synergistic performance. Where such assemblies require bonding of the plastic and glass elements together by an optical cement, difficulties sometimes arise in establishing or maintaining a physically firm and stable bond between the plastic element and the glass element. That is to say, the plastic and the cement are incompatible in the sense that sooner or later any bond initially established between them may be adversely affected in a manner impairing its optical neutrality. For instance, while as a rule stable bonds may be established between glass elements and optical cements, it has been found that the bonding of plastic elements by optical cements to glass elements or other plastic elements is often impaired by partial or total separation, crazes, fissures or cracks in the cement, etc., for reasons sometimes rooted in their different coefficients of expansion under conditions of changing temperatures or, generally, because of their lack of compatibility. Attempts to improve such bonds between optical cements and plastic lens elements by applying to the surfaces of the plastic lens elements wetting agents as primer layers have hitherto failed to yield satisfactory results.
It is, therefore, an object of the invention to make possible a stable physical bond, by means of a cement, between lens elements comprising plastic and glass, respectively.
Another object of the invention resides in the provision of a substantially stable bond of substantially permanent optical neutrality between lens elements of the kind referred by a room temperature vulcanizable cement.
Yet another object of the invention is to provide permanent adhesive bonds of physical stability between glass and plastic lens elements by simple and inexpensive means.
A still further object of the invention is to provide an improved bond between a cement and a plastic lens element which remains stable even over wide temperature ranges.
Other objects of the invention will in part be obvious and will in part appear below. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following specification.